Don't sleep on Matthew McConaughey's biggest relationship secret.

The Academy Award-winning actor, who has been married to wife Camila Alves for 13 years, has a simple recipe for maintaining a healthy marriage. 

McConaughey, 55, put pen to paper and offered a few of his life lessons in his new book, "Poems & Prayers." He told Fox News Digital that one small change in his household helped him further connect with the lady in his life. 

In an excerpt from his new book, McConaughey encouraged couples to downsize their mattress to "get ahead."

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"The best thing you can / do for your / marriage," he penned. "One way to surely / get ahead, / is get rid of that / king-­size mattress, / and sleep in a / queen-­size bed."

McConaughey delved into the reason why a smaller bed could provide a more fruitful connection.

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"We have kids and we go to our friend's house and he has one of these double king-size beds put together and all the kids sleep in the bed," McConaughey told Fox News Digital. "The wife's on one side with her side table and the husband's on the other side and it's great when you got all three kids, but all of a sudden the kids get too big. They're out of the bed."

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"I wake up one morning … I'm looking over there and Camilla's like a football field away man. Then you go to bed at night, like you want to snuggle up and … ‘Well, we’ve got to cover you up. Come about 12 feet and I'll come 12 feet.'"

He added, "You're like, man, this damn king-size bed is not good for the marriage, man. Get rid of that son of a b----. So we got a queen size where we're shoulder to shoulder. I'm telling you, it's good for your marriage."

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The "Dazed and Confused" actor noted that there's "no room" for any kids in the bed.

Themes throughout McConaughey's latest written work include love stories, faith, doubt, compassion and forgiveness. "Poems & Prayers" features writings inspired by both proverbs and the Old Testament, in addition to intentions and words of affirmation. 

Maintaining healthy family relationships not only as a father to three children, but also as a partner to Camilla, is important to McConaughey.

When McConaughey and Camila married in 2012, the family moved from California to Texas. The couple share three children: Levi, Vida and Livingston.

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"You've got kids, so you don't … you're spending as much time being a good mother and father of them, but you also gotta make sure – and I can do a better job of this – of going, ‘No, this is our time.’ You can't 100% live with the kids as a parent," McConaughey said. 

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"You gotta make to remember that one of the best examples you can give the kids of how to treat a woman or a man or how to someone they end up falling in love with down the line is how you treat their mother and how the mother treats the father."

Alves and McConaughey are so committed to finding time for each other that they launched their own alcohol brand in 2023, Pantalones Organic Tequila. They regularly star in cheeky campaign ads for the company, which offers three varieties of tequila.

"We enjoy ourselves," McConaughey said. "You know, like the tequila, we put damn good juice in a bottle. We were formal. We were buttoned up on that. As soon as we got good juice and a bottle, he said, pants off."

"Let's have a good time with the ads."

"Poems & Prayers" is available now.